Variable transformer



July 18, 1950 F. G. LOGAN VARIABLE TRANSFORMER July 18, 1950 F. G. LoGAN VARIABLE TRANSFORMER 2 Sheets-Sheet 2 INVENTOR /w/wf 6I 066A/ BY K QSQW July ATTOR EY Filed May 12, 1945 Patented July 18, 195

VARIABLE TRANSFORMER Frank G. Logan, Mount Vernon, N. Y., assignor to Ward Leonard Electric Company, a corporation of New York Application May 12, 1945, Serial No. 593,344

8 Claims.

This invention relates to improved controlling apparatus particularly useful for changing the voltage applied to a consumption circuit over a wide range, such as in dimmer control of lighting circuits in theaters and the like, and for various other purposes. The invention embodies an improved form of structure of an auto-transformer connected to a supply circuit wherein the voltage applied to the consumption circuit is changed by adjustment of a movable contact and is applicable to various forms of inductive windings.

The usual form of auto-transformers with an adjustable contact movable over adjacent turns of the winding has been limited to units of comparatively small capacity, mainly on account of excessive heating of the adjustable contact and of the windings of the transformer. Another objection is they are not durable or dependable in long continued use, except for small capacities, owing to insufficient area oi contact surfaces, displacement of the turns of the winding, breakdown of the insulation between turns and variation of the contact engaging surfaces. These objections are overcome by the present invention in a form of structure which is applicable to units of large, as well as small capacity, for various uses.

The main object of the present invention is to produce a form of structure which will be durable and dependable under long continued use. Another object is to produce a structure which is adapted for units of large current carrying capacity. Another object is to avoid objectionable heating by providing ample contact surfaces displaced from the winding so that the heating at the contacts will not effect the winding and the heating of the winding will not affect the contacts. Another object is to provide a structure wherein the heat from the Winding, brushes and contacts are readily dissipated. Another object is to so relate the contacts to the winding that the Winding and the insulation of its turns will be unaffected throughout long continued use. A further object is to provide a structure capable of wide range of output voltage from the maximum of the applied voltage to zero and to provide small changes in the output voltage by adjustment of the movable contact throughout the entire range of control. These and other objects and advantages will be understood from the following description and accompanying drawings which illustrate a preferred embodiment thereof.

Fig. 1 is a rear elevation, the rear cover plate being removed. and partly in section; Fig. 2 is a sectional view on line 2 2 of Fig. 1; and Fig. 3 is a sectionalview on line 3 3 of'Fig. l.

Referring to Fig. 2 a circular iron core 5 1S of laminated form with the laminations extending in an axial direction and built up by winding a ribbon of iron or steel on itself from the inner diameter of the core to the outer diameter. The inner and outer sides of the core are covered by sheets 6 of insulating material having their inner and outer edges bent over the edges of the core to form a base on which the winding I is wound. This winding may be of enameled insulated copper wire, such insulation or any similar form, serving to more effectively dissipate the heat from the winding. The inside and Outside dimensions of the core are preferably related so that the turns on the inside of the core are bank wound while those on the outside portion of the core are adjacent to each other and form a continuous single layer, except for a small uncovered portion at the top of the core as shown in Fig. 1.

The auxiliary xed contacts 8 are in the form of metal strips distributed around and extending in a radial direction from the winding within the plane of the winding and are preferably of hard brass. As shown in Fig. 2, they have an elongated main central portion with an outer end 8a bent at right-angles to the main portion and an offset inner end Bblextending toward the winding. These contact strips are shaped to have a comparatively wide contacting surface' on the face of the main portion, as shown in Fig. 1 and are tapered slightly from the outer end toward the inner end so that the edges of the main contacting surface upon which the brushes ride are radial to insure all of the brushes making contact substantially simultaneously as the brushes advance towards a higher voltage contact. As shown in Fig. l, the necks of the contacts are tapered so that the innermost ends have a width about equal to the diameter of the Wire of the winding 1. The inner end of each strip 8 has a cut-away semi-circular portion for directly engaging and embracing a turn of the winding l and is soldered thereto. In the particular form shown, the successive contact strips are secured at their inner ends to alternate turns of the winding, as shown in Fig. l, although in some cases they may engage successive turns or every third or fourth turn but the engagement of alternate turns has been found satisfactory in securing sufficiently small changes in the increase or decrease of the output voltage as the movable contact is adjusted. The fixed contacts are con- 3 nected to about the mid-portion of the outer part of the turn of the winding. In order to remove the insulation from the alternate turns where the contacts are to be Joined thereto. the alternate turns which are not to be' connected to the contacts are depressed at their mid-outer portion toward the core which leaves the other alternate turns projecting slightly therefrom. The insulation may then be ground oil! from the projecting alternate turns to give a small exposed portion of the wire of each alternate turn. 'Ihe inner ends of the fixed contacts may be soldered to these exposed surfaces respectively. The bentI outer end of Aeach contact strip is perforated to form a small opening lc, as shown in Fig. 2. The front portion of the apparatus is covered by a sheet metal plate 9 shaped as shown in Fig. 2 with an outwardly depressed central portion and an inwardly extending outer portion for enclosing the parts. The inside of the cover is provided with a lining of adhesive insulating material such as vitreous enamel or cement Ill. In forming and maturing this insulated ground coat. the cover is placed in a horizontal position and the insulating material applied over its inner surface. The wound core and its fixed contacts l are then partially immersed in the insulating material so as to embed the front portion of the winding ll and a portion of the inner ends of the contact strips 8 and also a portion of the outer ends of the contact strips. The insulating material passes into the openings Ic of the contact strips and thereby aids in holding the outer ends of the strips firmly in position. The insulating material which embeds the parts just described is then matured in a furnace or dried or otherwise treated for forming a firm union of the winding and contact strips to the front cover plate and securing a fixed position oi' the strips with reference to the winding by direct engagement of the supporting means with the strips and the winding. The contact surfaces of the contact strips are then ground down cientlyA to give a smooth, even surface for engagement by the movable contacts.I

The movable contact assembly is carried on the outer end of a sheet metal contact Ml.

Its innerend is insulated from and encircles the drive shaft IId. 'I'he edges of the contact II are bent at right-angles for stiness. The outer end of the arm is inclined somewhat to the main portion for the purpose ol bringing the contacts in alignment with the fixed contacts. Near the outer part of the arm a portion IIa is stamped out and bent inwardly and likewise the outer end I Ib of the arm is bent inwardly opposite the portion IIa. These parts serve to carry the movable contact assembly. A cross-pin I2 is supported at its ends on the inner portions of the parts IIa and IIb. Several brush blocixs i3, of molded insulating material, four being shown, are pivotally mounted at their ends on the pin I2 as shown particularly in Fig. 3. The other end of each block carries an outwardly extending metal pin Il which is molded in place at one end portion Within the block il. A metal brush holder I5, preferably of hard brass, is pivotally mounted on the extending portion of the pin I5. This brush holder is of channeled or U form and has oppositely extending end portions I5a and I5b. The portion lia is bent on itself and is threaded to receive a screw itc. An electrical connection from the brush holders to the contact arm is obtained by exible lead wires I6 which are respectively connected at one of their ends to a brush holder and at the other ends to the contact arm. One end of'each lead I8 is clamped between a washer and the extension lia of the brush holder and the other end is clamped between a metal strip il and the contact arm, the strip il being clamped in position by the screws ila. The brushes i@ are of carbon of rectangular form and fit tightly within the channel-shaped brush holder to form good electrical contact therewith. The inner end faces of the brushes engage the fixed contacts il and in Fig. 3 are shown slightly wider than the width of the contact strips and serve to solely engage one contact strip or to make a. bridging connection between adjoining contact strips. A helical spring i9 encircles the pin It between the inner side walls of each brush holder. The ends of the springs engage the top and exposed portions of the brushes for insuring their being held in place against the sides of the brush holders and against the fixed contact strips. This open channeled form of brush holder with extended end portions serves to dissipate heat from the brushes, giving free access of air to the brushes and also providing comparatively large heat dissipating surfaces on the brush holders.

The brush blocks i3 are spaced from each other by intervening washers on the pin l2; and a spring 2Q. as shown in Figs. 1 and 2, encircles the pin is between the portion lla of the contact arm and the brushes for yieldably forcing the brush blocks along the pin toward the portion lib of the contact arm for the purpose of keeplng the brushes in proper radial position with reference to the xed contacts. Another pin 2i entends between the portions lla and Mb of the contact arm and is parallel to the pin l2. Springs 22 at each of their ends engage respectively indentations in the back of each brush block i8 and pass around the pin 2l and then engage at their other ends the strip il. Each brush block lil is thus yieldably and individually pressed by its respective spring to force its brush holder and brush against the xed'contacts. Also the pivotal mounting of each brush holder on its pilot pin Ml permits movement thereon to secure self-alignment of the contact surfaces in any position of the parts. The carbon brushes have a negative temperature coefficient of resistance and. therefore there would be a tendency for the dierent brushes not to proportionally carry their proper share of the load current and in order to odset this, the connecting leads l@ are made of a metal having a high temperature coemcient of resistance such as iron, nickel or any other such metal. Thus any change in resistance of the carbon brushes is counter-acted by .the change of resistance of the leads IG and the several brushes are thereby forced to divide the load current within tolerable limits.

As shown in Fig. 2, the inner end of the contact arm ll ts over and is supported by a awed hub 253 of molded insulating material which hub nts on the shaft lid and is movable therewith. A drive arm 2d of sheet steel has a driving engagement at its outer end with the contact arm and is fixed at its inner end to the shaft iid. Near the outer end of the drive arm is riveted a steel pilot pin 25 which projects towards the contact arm. This pin is surrounded by a nged bushing 2t of molded insulating .materiaL the central inner portion of which nts within a circular opening in the contact arm. Thus the contact arm is insulated from the drive arm by the bushing 2t and from the shaft lid by the bushing 23. The flange of the bushing 23 is provided with a pair of outwardly projecting pins 23a which engage circular openings in the drive arm for locking these parts together. The driving connection between the shaft Hd and the arm 24 is secured by forming slots diametrically opposite and along the inner end of the shaft, the inner end of the arm 24 being provided with opposite inwardly projecting portions 24a which fit in the slots of the shaft. A steel washer 21 is welded to the inner end of the drive arm for securing increased strength of the driving connection with the shaft, the washer having opposite inner projections or keys 21a which engage the slots in the shaft. The inner end of the shaft is threaded and a nut 28 on the shaft holds the parts in place. An elongated keyed cross-piece 29 having outwardly bent ends 29a is mounted on the inner end of the shaft to form a coupling with a similar controlling device in alignment therewith when one or more of these devices are to be operated in common. A keyed washer 29h is welded thereto for additional strength and a nut 30 clamps the coupling in place. It will be appreciated that by the provision of the driving arm 24 having a strong engagement with the shaft Hd and by the driving connection with the contact arm being at a considerable distance from the shaft, the contact arm is actuated without imposing severe strains thereon and is well insulated from the driving parts.

A flanged bushing 3| of molded insulating material embraces the drive shaft Ild adjacent to the bushing 23 and is provided with an inner lining 32 of bronze or other suitable material for forming a bearing surface between the shaft and the bushing 3l. A collector ring 33 surrounds the flange of the bushing 3| and is provided with a at circular contact portion 33a on its rear face and with a curved outer flanged portion 33h, A projection 33e extends from the upper edge of the flange 33h to which projection a terminal lug 34 is secured by a screw 34a and washer connection. At the end of the contact arm are fixed a pair of circular brush studs 35, as shown in Figs. 1 and 2. These studs may be of brass and are provided with central reduced connections which project through openings in the contact arm and are fixed to the arm by a nut and washer connection engaging the neck of the studs. These studs slidably t within a pair of circular openings of a collector brush 36 of brass or other suitable composition. The inner surface of the collector brush engages the contact face portion 33a of the collector ring. The brush studs are each provided with a central opening in which are located springs 31, the inner ends of which springs engage the bottom of the openings in the collector brush for forcing the brush in good self-adjusting contact position against the collector ring.

A flanged bearing 38 of brass or other suitable material is mounted on the shaft outside an indented central portion of the plate IEl, the reduced portion of this bearing being adapted to slidably engage the inner end of the bushing 3|. Three long screws 39 extend longitudinally through the bushing 3| and their threaded endsengage the bearing 38. The tightening of these screws draws the bearing 33 against the cover 3 and draws the bushing 3| and collector ring 33 outwardly and thereby clamps the collector ring against the winding l, thus holding the co1- lector ring in a fixed position.

A cast-iron pulley 40 is xed to the shaft i Id outside the cover 9 for actuation of the contact arm when desired by a chain drive. At the inner end of the pulley 40 is fixed by the screws 40a a sheet metal pointer 4l for indicating the position of the contact arm and is in alignment therewith. A portion of the cover 3 is indented outwardly tc form a projection 9a to serve as a stop for the pointerv in its limiting positions. A handle 42 of molded insulating material is removably coupled to the pulley 40 in any suitable manner for turning the shaft and the drive arm and contact arm to any desired adjusted pition.

A rear cover 43 is removably secured to the rearwardly extending portions of the front cover 9 and these two covers are provided with upper central extended portions to receive a top sheet metal housing 44. Within the top housing a terminal block 45 of insulatingcmaterial rests upon and is secured to the top rearwardly extending portion of the cover 9. This block carries terminal bolts and connections 46a, 4Gb and 46c which are adapted to receive the external leads and which project downwardly through the terminal block. At the lower ends of the bolts connecting lugs 41 are provided for receiving the lead connections from the apparatus. Thus the lead 48a extends from the connection 46a to one end of the winding 1 and the lead connection 48e extends from the connection 46c to the other end of the winding 1 and the lead connection 48h extends from the connection 46h to the lug 34 mounted on the collector ring 33. It is apparent that with the supply connections made to the terminals 46a and 46c and with the output connections made between the terminals 4Gb and 46c, any desired intermediate output voltage may be obtained by adjusting the contact arm between the zero limit and the maximum voltage.

It is apparent that the structure described is of a sturdy character with ample contact areas between the movable contact assembly and the fixed contact strips displaced apart from the winding and adapted for carrying currents of large capacity. Likewise the heating at the brush contacts is segregated from the heating of the windings and by reason of a portion of the winding and a portion of the xed contacts being embedded in the insulating material In on the inner face of the front plate 9, ample provision is made for rapid dissipation of the heat. It is evident that this type of structure has many other advantages over the usual form of adjustable contact transformers.

Although a particular embodiment of the invention is shown and described herein, it will be understood that various modifications may be made for adaptation to particular purposes without departing from the scope thereof.

I claim:

1. A variable transformer comprising a core of circular form, a winding thereon, auxiliary fixed contact strips joined at their ends directly to turns of said winding and extending in a radial direction from the winding and within the plane of the winding, each of said strips having offset ends, means for securing said offset ends in fixed position with reference to said winding, said means directly engaging said ends and said winding, and movable contact means for successively engaging said strips.

2. A variable transformer comprising a core of circular form, a winding thereon, auxiliary xed contacts having their ends joined/directly to said winding and extending in a radial direction therefrom and within the plane of the winding, movable contact means for successively engaging said xedcontacts, a supporting plate, and insulating material between said plate and said winding and fixed contacts for supporting said winding and fixed contacts in fixed position, portions of said Y winding and portions of said fixed contacts being embedded in said insulating material.

3. A variable transformer comprising a, core of circular form, a winding thereon, auxiliary fixed contacts having their ends joined directly to turns of said winding and extending in a radial direction therefrom and within the plane of the winding, each of said contacts having oilset end portions, movable contact means for successively engaging said fixed contacts, a supporting plate, and insulating material between said plate and said winding, said offset end portions of the fixed contacts being embedded in said insulating material.

4. A variable transformer comprising a circular core, a winding thereon, fixed contact strips having their inner ends joined directly to turns of said winding and extending radially therefrom and Within the plane of said winding, movable contact means for successively engaging said contact strips, a supporting plate, insulating material between said plate and said winding and said contact strips for supporting' the winding and contact strips, said winding` and contact strips being partially embedded in said insulating material, a contact arm for actuating said contact means, and a central shaft extending through said plate for actuating said contact arm.

5. A variable transformer comprising a circular core, a winding thereon, fixed contact strips having their ends vJoined directly to turns of said winding and extending radially therefrom and within the plane of said'winding, movable contact means for successively engaging said strips,

a contact arm for actuating said means, a fixed collector ring between said winding and said contact arm, said contact arm having means for electrically connecting said arm to said collector ring in any position of said arm, and a centrall circling -said shaft and engaging a portion of said winding, means for clamping said vring against said winding and toward said plate, and

a contact arm actuated by said shaft for carrying said movable contact means at one end and for carrying contact means at its gaging said ring. A

7. A variable transformer comprising a circular core, a winding thereon, contact strips having their ends Joined directly to turns of said winding and extending radially therefrom and within the plane of said Winding, movable contact means for successively engaging said contact strips, a supporting plate, insulating material between said plate and said winding and strips for supporting them in iixed position. a portion of said winding and a portion of said strips being embedded in said insulating material. a central actuating shaft, a collector ring encircling said shaft and clamped in fixed position against said winding, a contact arm forcarrying said movable contact means at one end and 'a collector brush at its opposite end in engagement with said collector ring, and a driving arm fixed to said shaft and having a driving connection with said contact arm at some distance from said shaft.

8. A variable transformer comprising a circular core, a winding thereon. a series of contact strips electrically connected to turns of the winding and extending in a radial direction from the `winding and within the plane of the winding, movable ,contact means for successively engaging said contact strips, a supporting plate, and adhesive in sulating material between said plate and said winding and between said plate and said contact strips for supporting said winding and contact strips in fixed relative positions to each other on said plate, said winding and contact strips being partially embedded in said insulating material.

FRANK G. MAN.

`BltlilERlERiilES Cll'llEiiD The following references are of recordl in the ille of this patent: 1

UNITED STATES PATENTS s Germany Sept. 29, i922 other end/'for en- I 

